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Mobile & Wireless
The R6 interface and the open standards debate
Openness will help drive lower costs and more end-user services
by Mano Vafai, WiMAX Forum® Application Architecture
The value of WiMAX is becoming widely recognized as service providers
solidify their plans and start delivering high-bandwidth mobile internet
services over a lower-cost WiMAX infrastructure built on open
interfaces.
These deployments are a win-win for both service providers
and consumers — end users can access more services, while service
providers have a cost-effective way to gain revenue.
The demand for WiMAX has also set into motion the convergence of
consumer electronic and mobile technologies. Companies like Intel, with
plans to embed WiMAX-compatible chips in every laptop by the end of
2008, are betting on widespread adoption. Semiconductor companies are
also building specialized WiMAX chips for consumer goods such as
cameras, navigation tools, gaming and entertainment devices. Efforts are
also underway to bring this technology into offices and homes cost
effectively through picocell or femtocell base stations. Such devices are
focused on high-volume, mass-market, plug-and-play deployment models
to drive very low cost points.
With all the right pieces coming into place, consumer expectations for
WiMAX will be extremely high. Consumers will demand more services and
lower prices than current 3G technologies such as EVDO or High Speed
Packet Access (HSPA) provide. And service providers are betting on a
much lower infrastructure cost to build a long-term profitable business.
They want to be able to negotiate for the best price/performance
products in the market, and they want infrastructure equipment from
multiple vendors to work seamlessly with their networks.
Achieving these objectives is only possible through open standards and
bullet-proof Interoperability Tested (IOT) reference points at the air
interface and at the strategic interfaces to all other network elements.
Open standards are critical to delivering cost-effective infrastructure
and end devices that will drive overall demand for WiMAX.
Need for open standards
The debate over standards is confusing, but the outcome can have far-
reaching implications for mobile service providers making decisions about
WiMAX technologies. Depending on the outcome, many face the
prospect of dealing with a closed, proprietary architecture that could
significantly inflate costs and limit their options.
In WiMAX, the critical R6 interface between base stations and Access
Service Network (ASN) Gateways enables the WiMAX radio network and
the core IP network to interoperate, thus ensuring service providers can
choose best-of-breed solutions. Without an open interface, mobile
service providers must work with a single, proprietary solution when
building out their WiMAX network.
The WiMAX Forum® is taking steps to define standard interfaces and
IOT certification, and to recommend additional steps needed for a
mandatory R6 reference point. This is crucial for developing a true open
WiMAX standard.
Since 802.16 focuses mainly on the wireless air interface level, the
WiMAX Forum set up a Network Working Group (NWG) to create higher-
level networking specifications for fixed, nomadic, portable and mobile
WiMAX systems, which will enable economy of scale and standardization
for large-scale WiMAX deployments. The NWG has developed five open-
interface reference points: R1, R2, R3, R4 and R5. (See Figure 1. WiMAX
Network Key Interfaces)
For the R6 interface, however, the NWG developed three separate
profiles – A, B and C – and this has become a subject of confusion and
debate. Profiles A and C expose the R6 interface, whereas Profile B
neither defines the R6 interface nor exposes it for interoperability.
Logically, Profile B does not seem to be a standard profile.
While some in the industry have focused on Profiles A or C, some large
vendors back Profile B because it lets them hide their proprietary
network architectures under the umbrella of a standard. In short, Profile
B forces operators to buy ASN Gateways and base stations from the
same vendor, which prevents them from leveraging the value of mixing
and matching best-in-class products and limits their network
functionality. Profile B also prevents operators from leveraging their core
equipment for supporting off-the-shelf picocell or femtocell base stations
that would become available with an open R6 interface.
CWG steps up
The Certification Working Group (CWG) of WiMAX Forum is developing a
certification program for WiMAX technology to recognize equipment that
has successfully passed a defined set of tests and hence has a certain
level of performance and interoperability. The Wave 2 WiMAX
certification program is concerned with two major areas:
- Radio Conformance Test at the 802.16 Physical level (RCT)
- Protocol Conformance Test at the 802.16 MAC layer (PCT)
In addition, the WiMAX Forum’s Network Interoperability Testing (NWIOT)
special task group focuses on ensuring interoperability across all
reference points (R1 through R6) defined in NWG specifications:
- MS/CPE Interoperability with WiMAX Networks (R1, R2)
- Inter-ASN Interoperability (across R4 and R3)
- Interoperability between base stations and ASN gateways, when R6 is exposed
From a practical perspective, test observation points are required for
controllability and for the ability to observe, and this is only possible with
Profiles A and C, which have simple and open interfaces. End-to-end
testing and plug-and-play scenarios are inconceivable with the
proprietary R6 interface of Profile B. Multiple profiles would also reduce
the number of qualified vendors needed for profile validation, given that
the extensive process consisting of test development, validation and
maintenance is too cumbersome.
R6’s strategic importance
The R6 is the most important interface in the commercial rollout of
WiMAX networks. In a typical WIMAX network, just one ASN Gateway
can support hundreds of base stations and impacts overall functionality
and services over the wireless networks. As the network grows,
operators will add more picocells and femtocells, especially in dense
urban areas with high concentrations of traffic, which could amount to
thousands of R6 interfaces per network. Exposing and standardizing this
interface should thus become the highest priority for network
standardization efforts.
R6 is closely related to performance-dependent events such as handover, paging and idle mode, and more. An open R6 interface is critical for operators that want to leverage the benefits of
an open marketplace and ensure scalability, innovations and competitive
cost structures. Within this scenario quite a few issues need to be
ironed out, such as network management, Operations and Maintenance
(OAM) and timers. Time is of the essence here; the WiMAX Forum needs
to focus on maturing one R6 interface suitable for both IOT and open
WiMAX Network certification.
Open WiMAX networks
Currently R1, R2, R3, R4 and R5 are exposed and uniquely identified
regardless of the ASN Gateway profile type. A unique and mandatory R6
interface could greatly help end-to-end interoperability of WiMAX, and
with its economy of scale, help service providers around the globe to
penetrate larger markets and larger parts of the population. WiMAX
operators have recognized the potential of an open R6 interface and are
now explicitly asking for an open R6 interface. They are ruling out the
proprietary Profile B to avoid risking the future scalability of their
networks by getting locked into a proprietary vendor solution. Profile C
seems to be the most popular profile among operators. Moving to this
single interface would simplify network IOT and accelerate a real open
standard, resulting in the following benefits:
- Interoperability and multi-vendor support
- Architecture enhancement simplification
- Fewer architectural options
- Economies of scale
- Operators would have more choice in vendor selection
- Vendors would have more market opportunity to sell
- Reduced preparation and cost of tests, as more vendors will utilize the same profile
As the standard evolves, some of the network intelligence from Profile A,
such as macro load-balancing and interference management, can be
added to Profile C, with full backward compatibility with the current
Profile C R6 interface to protect operator and vendor investment in
Profile C.
What will be required to enable wireless operators to build open WiMAX
networks, is one common profile that enables operators to mix and
match network elements from multiple sources. The proprietary and
vendor-specific Profile B advances the principle of closed and proprietary
networks, enabling an equipment vendor to lock up an operator’s
network and preventing the operator from enjoying the lower costs and
innovative technology that come from fostering a more competitive
environment.
The WiMAX Forum should focus on breaking the classic 2G/3G closed architecture model and standardize on Profile C only. This will enable operators to deploy radio and network equipment from different vendors based on a single R6 interface. Profile C will foster
innovation and ensure that WiMAX equipment will be competitively priced
to allow operators to build their networks cost effectively.
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